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Chapter 1: Analysis of Complex Electrophysiologic Data

INTRODUCTION

A novice in a busy electrophysiology (EP) laboratory will generally learn to recognize common arrhythmias in a relatively short time. It requires considerably more seasoning to recognize the variants and unusual mechanisms, or to “hit the curve ball.” It is hoped that the following commentary helps provide structure and focus to the EP study and facilitates analysis of the case studies to follow.

IT BEGINS WITH THE ELECTROCARDIOGRAM

The EP study is an extension of the electrocardiogram (ECG) with the addition of intracardiac recording and programmed electrical stimulation. Insightful interpretation of the ECG allows for prospective consideration of additional catheters, stimulation sequences, or maneuvers appropriate for the postulated arrhythmia. This interpretation limits the diagnostic possibilities and avoids unnecessary steps (Case 1–1). The fundamentals of ECG interpretation of an arrhythmia include the identification of P waves, determining the atrioventricular (AV) relationship, and analyzing the QRS morphology (Table 1–1). For confusing problems, it helps to create a “written” list of all potential hypotheses and to plan for specific interventions that will test them. As data are accumulated during the EP study, the facts supporting or refuting the hypotheses can be tabulated. The hypotheses can be represented by schematic drawings for complicated scenarios. This method is illustrated at the end of this chapter.

1–1

Two-channel rhythm strip recorded from a patient scheduled for electrophysiology study for palpitations. The onset of the tachycardia occurs after the second QRS and the P wave is noted in the following diastole to be of different morphology than the probable initial sinus P wave. The identification of the P wave during tachycardia is facilitated by comparison with the last QRS in the strip that is not followed by a P wave. Careful measurement with calipers (a critical tool of the electrophysiologist) will illustrate that the onset of the tachycardia does not require PR prolongation. In addition, the cycle length varies and during this process, the PR stays constant while the apparent RP varies. These findings are most compatible with an atrial tachycardia. Note that most junctional reentrant tachycardias would require some AV delay at the onset, and such variable retrograde conduction would be unusual. This information provides a focused starting point to plan electrophysiology study.

An electrocardiogram (ECG) rhythm strip showing a patient’s heart activity during an electrophysiology study for palpitations. The strip reveals the onset of tachycardia after the second QRS complex, with a distinct P wave appearing in the following diastole, differing in morphology from the initial sinus P wave. The identification of the P wave during tachycardia is aided by comparing it with the last QRS complex on the strip that lacks a subsequent P wave. Caliper measurements are used to demonstrate that the onset of tachycardia does not involve PR prolongation. Additionally, the cycle length varies while the PR interval remains constant, leading to variable apparent RP intervals. These findings are indicative of atrial tachycardia, as they differ from the characteristics typically associated with junctional reentrant tachycardias, which typically involve some AV delay at the onset and less variable retrograde conduction. This information serves as a valuable starting point for planning an electrophysiology study.
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Table 1–1ECG Rhythm Analysis
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Table 1–1 ECG Rhythm Analysis

  • Identify P waves and determine their morphology, if possible

  • Determine the atrial rhythm

  • Analyze the QRS complex morphology

  • Determine the A–V relationship

LESS IS OFTEN NOT MORE

There are those gifted, intuitive individuals who leap to the correct diagnosis and apparently bypass all the rational, systematic steps. Most of us, however, are better served by a consistent, methodical approach that does not cut corners. A sample protocol for an ...

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